Base62 encoding for arbitrary precision integers

go get



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base62 implements base62 encoding for integer numbers of arbitrary precision.

Currently both int64 and *big.Int are supported


The encoding is different to base64 encoding in two ways:

  • Reduced character set, without symbols - 0-9A-Za-z
  • Character ordering - base64 is A-Za-z0-9

Note that this character ordering is also different to most other base62 encodings, but preserves the sort order of encoded values.

As a result, the encoded strings can be lexically sorted if either a sorting order such as shortlex is used, or if the resulting strings are left padded to ensure a consistent length.


First go get the package:

go get

This can then be used as below:

package main

import (

func main() {
    // Encoding 64 bit integers
    var n int64 = 4815162342
    encoded := base62.EncodeInt64(n)
    fmt.Println(encoded) // prints 5Frvgk

    // Arbitrary precision integers can be specified using the math/big pkg
    var b *big.Int = new(big.Int)
    b.SetString("340282366920938463463374607431768211455") // 128bit unsigned int
    bigEncoded := base62.EncodeBigInt(b)
    fmt.Println(bigEncoded) // prints 7n42DGM5Tflk9n8mt7Fhc7

    // Padding can be specified using an option on an Encoding
    // eg. to pad strings to a minimum length of 15 chars:
    e := base62.NewStdEncoding().Option(Padding(15))
    encoded = e.EncodeInt64(n)
    fmt.Println(encoded) // prints 0000000005Frvgk